Purebred and Hybrid Electric VTOL Tilt Rotor Aircraft

ABSTRACT

Electrically powered Vertical Takeoff and Landing (VTOL) aircraft are presented. Contemplated VTOL aircraft can include one or more electrical energy stores capable of delivering electrical power to one or more electric motors disposed within one or more rotor housings, where the motors can drive the rotors. The VTOL aircraft can also include one or more sustainer energy/power sources (e.g., batteries, engines, generators, fuel-cells, semi-cells, etc.) capable of driving the motors should the energy stores fail or deplete. Various VTOL configurations are presented including an all-battery purebred design, a light hybrid design, and a heavy hybrid design. The contemplated configurations address safety, noise, and outwash concerns to allow such designs to operate in built-up areas while retaining competitive performance relative to existing aircraft.

This application is a continuation of U.S. patent application havingSer. No. 12/693,657 filed Jan. 26, 2013 which claims the benefit ofpriority to U.S. provisional application having Ser. No. 61/147,499filed on Jan. 27, 2009. This and all other extrinsic materials discussedherein are incorporated by reference in their entirety. Where adefinition or use of a term in an incorporated reference is inconsistentor contrary to the definition of that term provided herein, thedefinition of that term provided herein applies and the definition ofthat term in the reference does not apply.

FIELD OF THE INVENTION

The field of the invention is tilt rotor aircraft technologies.

BACKGROUND

Currently available vertically capable aircraft (VTOLs) are generallydenied permission for routine powered terminal operations (e.g.,take-off, low altitude climb, landing, etc.) in populated, built-upareas for one or more of four reasons: safety, noise, exhaust emissions,or outwash velocity. Further, current rotary-wing VTOLs, except for veryadvanced tilt rotor aircraft, cannot compete with similar payload-class,fixed-wing, propeller-driven aircraft in speed and range whenunrestricted expansive take-off and landing facilities and climbcorridors are conveniently available at both ends of a mission. So thesimultaneous attainment of radically improved terminal safety, tolerablenoise and fumes, modest outwash velocity and competitive fixed-wingspeeds, efficiencies, and ranges would enable rotary-wing aircraft todominate the current light aircraft market, subject to pricedifferentials, and open up the vast denied market for terminaloperations in built-up areas. Two other factors, though not essential tocorrect the above rotary-wing shortfalls, add to the market expansionpotential for the subject electrically-powered rotor craft: (1)independence from logistically burdensome fuels (e.g., JP, H₂, etc.) atlight-duty bases, particularly in built-up areas, and (2) fullyautonomous flight control/management to relieve the stiff requirementfor specialized pilot proficiency, thus eliminating another disincentivefor vertical aircraft ownership/operation.

Although numerous low-performance electric fixed-wing aircraft have beenbuilt, the only widely publicized claims to an electric tilt rotoraircraft are made by FALX AIR™ Hybrid Tilt Rotor. To the degree thatpopular descriptions are accurate: (1) the configuration is a low aspectratio tilt-wing, not a tilt-rotor; (2) the batteries in the FALX AIR aresupplemental to the internal combustion engine to assistHover-Out-of-Ground-Effect (HOGE) and climb and do not provide separatefull HOGE power; hence, the FALX AIR lacks fully redundant power in thedead man zone for silent, safe takeoff and landing in built-up areas;(3) the dual electric motors/nacelle are insufficient at this moderatelyhigh disk loading to supply HOGE with one-propulsion-motor-inoperative(OPMI), thus severely compromising safety in built-up areas; and (4) theFALX AIR makes no pretense of basing-independence allowing all-electricoperation for basing in the absence of conventional logistic fuels.

Similarly, the Aurora Flight Science's™ Excalibur concept VTOL electrichybrid is not a tilt-rotor configuration, but rather a direct thrustturbofan, 70% of vertical lift, with supplemental electric ducted fanlift during HOGE.

Four recent advances in disparate technologies can synergize to enableefficient electric tilt-rotor VTOL aircraft. Tilt-rotor aerodynamic,structural, and propulsive efficiencies have improved. Extremelyflight-efficient tilt-rotor aircraft, far beyond the V-22's anemiclift-to-drag ratio, low propulsion efficiency, and high structuralweight fraction result in more than 2× the V-22's specificpayload×range. Electric motor power densities have increased.High-performance, light-weight electric motors and generators can havemore than three times the power-density of motors being introduced inelectrically propelled automobiles. Battery energy densities have alsoincreased and can provide energy densities of 100, 200, 300, or even upto 400 W-hrs/kg. Furthermore, autonomous flight control and managementsystems have dramatically improved. For example, autonomous flightcontrol and route/ATC management with pilot override, which allow fortotally autonomous flight from takeoff to landing have been demonstratedin the A-160 Hummingbird.

All of the above individual subsystem elements for a newelectrically-powered tilt-rotor VTOL (E-VTOL) have already beenseparately demonstrated: (1) Hardware has been demonstrated withprototypes of very high performance electric motors/generators,small/light/low-sfc turbines, moderately high performance lithiumbatteries, variable speed rigid rotors, light weight all-carbonstructures, and autonomous flight/management of rotary wing VTOLs. (2)Extensive vetting by independent parties of related aerodynamicallyefficient tilt-rotor airframe designs (though not with electricpropulsion architectures) has testified as to the practicality of theassumed aerodynamics and weights. (3) Finally, the very high-performancelithium batteries necessary for the purebred battery electricarchitectural variant are at the bench chemistry stage within theNational labs and less visibly with private firms, thus developable withexpected vigor.

What has yet to be appreciated is that the above advances can now becombined to realize many new capabilities that address issues with theknown art. The contemplated E-VTOL aircraft have tolerable noise, zeroemissions, or acceptable outwash velocity necessary for powered terminaloperations in populated, built-up geography. An E-VTOL aircraft hasvertical flight safety improvements to bring rotary-wing aircraft intoparity with fixed-wing competitors (e.g., factor of 10 reductions inaccidents per flight-hour) and makes vertical flight politicallycompatible with terminal operations in built-up areas, such aselimination of the “dead man's zone”. Electrically-powered,vertically-capable aircraft can have market-competitive speed and rangerelative to current personal, executive, light cargo, public safety, andmilitary fixed-wing, propeller-driven aircraft below 20,000 lb grossweight. Such aircraft also have the benefit of basing-independence fromconventional on-site liquid fossil fuel support for short rangeoperations where only electrical power would likely be required forrecharging batteries. The aircraft also have naturally low infra-red andacoustic signature in terminal operations where combat threats are mostprevalent. Contemplated designs also eliminate a requirement for atwo-speed gearbox or mechanical cross shafting that would ordinarily benecessary for optimized vertical lift, horizontal cruise rotor RPM, andsafe vertical terminal operations when separate rotor nacelles aredriven by conventional turbine engine mechanical drive trains. Designscan also include non-tilting sustainer engines in the electric hybridwhich avoid lubrication problems and engine design specialization intypical “engine-in-nacelle” tilt-rotor aircraft. Additionally electrichybrid VTOL (E-VTOL) have a wide flexibility in choice of sustainerenergy source types or sizes within the same airframe to suit thedesired cruise speed and altitude with no change in rotor electric drivemotors which are sized for vertical flight and hence over-powered forall but highest speed cruise.

The above advanced capabilities can be achieved using multiple electricmotors to drive each rotor through one or more fixed reduction gearboxesand a choice of at least three power supply architectures, all of whichenable full redundancy in both rotor drive motors and electric powersupply for safe, hover-out-of-ground-effect (HOGE) in built-up areas.All three are purely electric during quiet, emission-free operations inbuilt up areas. A heavy hybrid can be entirely electric, hencebasing-independent, for short range operations (e.g., less than 50nautical miles). A purebred battery architecture can be innatelyall-electric for full flight range (e.g., greater than 200 nm). A lighthybrid offers full range (e.g., on the order of 1000 nm) flight, but canrequire traditional logistic fuel availability under normal basingconditions even though it retains quiet, safe, all-electric terminaloperations capability. All designs benefit from fully autonomous flightcontrol with pilot override to reduce or eliminate pilot skillrequirements and further improve safety of this inherently complexvertical lift aircraft.

Therefore, there remains a considerable need for methods, systems, andconfigurations for providing VTOL tilt-rotor aircraft.

SUMMARY OF THE INVENTION

The inventive subject matter provides apparatus, systems and methods inwhich a vertical takeoff and landing (VTOL) aircraft is configured toachieve hover-out-of-ground-effect (HOGE) while under the power of anelectrical motor. One aspect of the inventive subject matter includes aVTOL heavier than air aircraft that includes one or more electricalmotors coupled to one or more rotors. The aircraft also includes one ormore electrical energy stores (e.g., a battery, fuel-cell, etc.) thatcan drive the motors. Preferably an electrical energy store can beconfigured to deliver at least 100 W-hrs/kg, more preferably at least200 W-hrs/kg, yet more preferably at least 300 W-hrs/kg, and even morepreferably at least 400 W-hrs/kg. Such aircraft can achieve HOGE for atleast four minutes while under power of at least one electrical motorand while carrying a payload of at least 50 pounds. In more preferredembodiments, the aircraft can achieve HOGE while carrying at least 100pounds, yet more preferably at least 1000 pounds, and even morepreferably at least 3,500 pounds. In some embodiments, the electricalenergy store can comprise a rechargeable battery. It is alsocontemplated that the battery could be repositioned to adjust the centerof gravity of the aircraft.

The aircraft can also incorporate one or more sustainer energy/powersources capable of supplying electrical power to the motors. Examplesustainer energy/power sources can include a fuel driven engine andgenerator, a fuel cell, a semi-cell, or other sources of electricalpower.

One should appreciate that contemplated VTOL aircraft can include aplurality of electrical motors. In some embodiments, the VTOL aircraftcan include multiple electrical motors coupled to respective rotors.Preferably, the electrical motors can support fail-over operation wherea first motor can service a second motor's rotor while the second motoris inoperative. In such embodiments the aircraft can achieve HOGE withone propulsion motor inoperative (OPMI). The motors can be deployedwithin tiltable nacelles, each nacelle having a corresponding rotor. Itis also contemplated that the nacelles could house one, two, or moreadditional redundant motors.

Various objects, features, aspects and advantages of the inventivesubject matter will become more apparent from the following detaileddescription of preferred embodiments, along with the accompanyingdrawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1A presents a schematic of a possible all battery purebredpropulsion architecture.

FIG. 1B presents a schematic of a possible “battery plus sustainer”heavy hybrid propulsion architecture.

FIG. 1C presents a schematic of a possible “battery plus sustainer”light hybrid propulsion architecture.

FIG. 2A presents a schematic of a possible maximal safety drivelinehaving three motors per nacelle.

FIG. 2B presents a schematic of a possible maximal safety drivelinehaving two motors per nacelle.

FIG. 2C presents a schematic of a possible intermediate safety drivelinehaving one motor per nacelle and an extra propulsion motor.

FIG. 2D presents a schematic of a possible minimalist safety drivelinehaving one motor per nacelle.

FIG. 3 represents a table listing desirable market-competitiveperformance parameters for various elements of a VTOL aircraft.

FIG. 4 presents a top view of a possible VTOL aircraft in hover mode.

FIG. 5 presents views of a possible VTOL aircraft when in verticalflight and horizontal flight.

FIG. 6 presents a side view of a contemplated VTOL aircraft andillustrates possible internal arrangements.

FIG. 7 presents a front view of a possible VTOL aircraft and illustratespilot and passenger positions.

FIG. 8 presents cross sectional view of a possible VTOL aircraft.

FIG. 9A represents a table outlining a weight breakdown of acontemplated light hybrid airframe VTOL aircraft.

FIG. 9B is a continuation of the table in FIG. 9A.

FIG. 10 represents a table of Hover-Out-of-Ground Effect (HOGE)performance.

FIGS. 11A and 11B present example wetted area and a graph illustratingapproximately the lift-to-drag of a possible VTOL aircraft relative toother existing aircraft.

FIG. 12 presents a graph illustrating lift-to-drag performance for atypical aircraft.

DETAILED DESCRIPTION

The present inventive subject matter is drawn to systems,configurations, and methods of providing numerous advances to VTOLtilt-rotor aircraft, especially electrically driven VTOL (E-VTOL).

The disclosed subject exploits advanced electric propulsion in concertwith highly efficient, autonomously piloted with pilot override VerticalTake-Off and Landing (VTOL) tilt-rotor aircraft to radically expand thesafe, legal, and practical ingress, egress, and basing into, out of, orwithin populated, built-up locales, and to achieve speeds and rangescompetitive with current fixed wing, propeller-driven aircraft of thesame payload class. While less efficient rotary wing aircraft (e.g.,helicopters and compounds) also benefit from the electric propulsion interms of safety and legality (e.g., noise or exhaust emissionsrequirements), their innately lower lift-to-drag ratios prevent themfrom competing with fixed-wing, propeller-driven aircraft in speed andrange.

Understanding the Concept

The inventive subject matter encompasses at least three fundamentallydifferent electric propulsion architectures (e.g., purebred battery;light hybrid; and heavy, basing-independent hybrid, etc.) which, whenmechanized on advanced, high-efficiency tilt-rotor vertical takeoff andlanding (VTOL) aircraft, substantially expand the performance envelope,safety, or basing options over that currently available withconventional helicopters and fixed wing aircraft against which theelectric tilt-rotor must compete.

An example VTOL aircraft that could be adapted to benefit from thedisclosed techniques could include the U.S. Government baseline HighEfficiency Tilt Rotor (HETR) design based on an Optimum Speed Tilt Rotor(OSTR) system as described in U.S. Pat. No. 6,641,365 to Karem titled“Optimum Speed Tilt Rotor” and industry designs revealed in a JointHeavy Lift (JHL) Intra-Theater Cargo Vertical Aircraft competition. Thisand all other extrinsic materials discussed herein are incorporated byreference in their entirety. Where a definition or use of a term in anincorporated reference is inconsistent or contrary to the definition ofthat term provided herein, the definition of that term provided hereinapplies and the definition of that term in the reference does not apply.

Table 1 summarizes various architectures of the contemplated designs.

TABLE 1 Silent, Clean Small Battery Energy Terminal Store for Basing-Sustainer Electric Operations Energy Independence and 50 nm PowerGenerator Sustainer Energy Store All-Electric Range for Cruise or FuelStore Purebred provided by Sustainer provided by Sustainer provided bysplit high energy Electric battery battery sustainer battery densityrechargeable battery Electric provided by ≧50 nm split highenergy-density engine/generator, gaseous, liquid, or rotor drive batteryrechargeable battery electric fuel cell, or solid replenishable heavyelectric semi-cell fuel hybrids Electric split high energy NotApplicable engine/generator, gaseous, liquid, or rotor drive densityrechargeable electric fuel cell, or solid replenishable light batteryfor takeoff, electric semi-cell fuel hybrids climb, and landing only

FIGS. 1A, 1B, and 1C illustrate several different notional electricpropulsion architectures with nominal subsystem efficiencies.

In FIG. 1A, propulsion system 100A represents an all battery purebreddesign. System 100A can include an electrical energy source asrepresented by split section battery 120A, which electrically couples toone or more of motors 114. Preferably battery 120A comprises one or morehigh energy density batteries, possibly having split sections forfailure isolation. Motors 114 are mechanically coupled to reductiongearbox 112, which in turn couple to rotor 105. Naturally, it should beappreciated that rotor 105 and motor 114 are configured to produce athrust force counter to the weight of the aircraft. As illustrated, theefficiencies of the system components are relatively high. As discussedfurther below, the contemplated configuration can provide for an E-VTOLcapable of achieving HOGE for at least four minutes while carrying apayload of at least 50 pounds. Various configurations provided belowalso provide for carrying payloads in excess of 100, 200, 500, 1000,3000, or even 3500 pounds.

In FIG. 1B, propulsion system 100B has similar components to system 100Aof FIG. 1A, with the addition of a sustainer power source 122B. System100B represents a battery plus sustainer heavy hybrid design. Sustainer122B represents a source of additional electric power capable of drivingone or more of motors 114. An additional sustainer 122B can electricallycoupled to batteries 120B. Sustainer 122B can be fueled from fuel tank130. The contemplated design allows for basing independence and up to 50nm pure electric flight without requiring additional sustainerassistance. In such embodiments, electrical energy store 120B cancomprise a rechargeable battery that can be recharged from sustainerpower source 122B, even during flight. It is also contemplated thatbattery 120B could be repositionable within the aircraft, possibly toprovide adjustment for the aircraft's center of gravity.

Sustainer power source 122B can take on many different forms. In someembodiments, sustainer 122B can include a fuel driven combustion enginepowering an electric generator. Sustainer 122B can also include one ormore fuel-cells or electric semi-cells. One should also appreciate thatsustainer 122B can also comprise combinations of various additionalelectrical power sources.

In FIG. 1C, propulsion system 100C is similar to system 100B, with theexception that the system represents a battery plus sustainer lighthybrid design. As with system 100B, sustainer 122C couple to batteries120C providing optional recharge of batteries 120C in addition toproviding power directly to electric motors 114. Alone Batteries 120Ccan provide sufficient power for terminal operations (e.g., taking off,landing, maneuvering, low altitude climb, etc.).

Myriad high energy density batteries are currently available having awide variety of applications. Such battery technologies can be adaptedfor use within the disclosed subject matter. Example batteries caninclude the BA 5590 Li—SO₂ battery produced by Saft™, Inc having anenergy density 250 W-hrs/kg. Another example battery can include the BA7847 Lithium-Manganese Dioxide battery having an energy density of 400W-hrs/kg offered by Ultralife Batteries™, Inc. It is also contemplatedthat Lithium-air exchangeable recyclable primary batteries based onLithium perchloride could supply energy densities in excess of 1000W-hrs/kg, where such batteries have a theoretical energy density greaterthan 3000 W-hrs/kg as discussed in “Lithium Primary Continues to Evolve”by Donald Georgi from the 42^(nd) Power Sources Conference, June 2006.One should appreciate that configuration of such commercially availablebatteries or configuration of other existing battery technologies foruse within contemplated VTOL aircraft is considered to fall within thescope of the inventive subject matter. For example, it is alsocontemplated that automotive plug-in hybrid can be adapted for use within the inventive subject matter. The batteries representing theelectrical energy store of the VTOL aircraft can also be configured tobe field-replaceable for ease of maintenance. Thus, a VTOL aircraftcould carry one or more spare batteries that can be swapped with afailed or failing battery in the field during a mission withoutrequiring a maintenance facility.

The previously discussed propulsion systems can be applied to numeroustypes of aircraft markets. In a preferred embodiment, the propulsionsystems can be directly applicable to rotary wing and fixed wingaircraft markets. For example, general aviation (e.g., personal, lightbusiness, executive business, public safety, light military, lightcharter, and light cargo class with 1-14 total seats or at least 3500lbs payload) aircraft would benefit from such designs by reducing noise,emissions, or other undesirable characteristics. Additionally, unmannedaviation with a gross weight of less than 20,000 lbs could leverage thedisclosed techniques.

Table 2 lists desirable cruise speeds and ranges for current fixed-winggeneral aviation markets. The disclosed designs provide complementarycapabilities for an E-VTOL aircraft.

TABLE 2 Range w/Powered Vertical Landing Cruise Speed ReservesPersonal >165 kts >200 nm Light Business >210 kts >800 nm ExecutiveBusiness >300 kts >800 nm Light Charter >340 kts >800 nm

FIGS. 2A, 2B, 2C, and 2D illustrate driveline options having variousdegrees of redundancy. The contemplated configurations can provide forachieving HOGE with one propulsion motor inoperative (OPMI), with theexception of the design presented in FIG. 2D.

In FIG. 2A driveline system 200A can comprise two of nacelles 240, eachhousing three motors 214A and combining/reduction gearbox 212, which inturn couple to rotors 205. In such an embodiment, energy source 220 cansupply triple propulsion motors 214A with sufficient continuous powerover cables 225 to achieve HOGE for at least four minutes. One shouldalso note that the additional motors 214A in nacelles provide redundancyto allow HOGE to be achieved while under OPMI. The configuration shownin FIG. 2A is considered to have a maximal safety driveline due to motorredundancy. Other configurations are also contemplated. As noted in FIG.2A each of propulsion motor 214A can have a co-locatedinverter/controller.

FIG. 2B provides an alternative configuration to that of FIG. 2A. Ratherthan having three motors per nacelle 240, driveline 200B comprisesdouble motors 214B per nacelle. This configuration also has redundantmotors, while preferably requiring that each of motors 214B havesufficient capabilities to achieve HOGE under desirable conditions.Although likely having less safety than driveline 200A depending on thecapabilities of motors 214B depending on the aircraft's designparameters, driveline 200B is also considered to have maximal safety.One skilled in the art will appreciate that selection of motors 214Bdepends on the class or requirements of the VTOL aircraft being built.

FIG. 2C presents possible driveline 200C considered to have anintermediate level of safety, while still being able to achieve HOGEunder desirable conditions. Driveline 200C includes a single motor 214Cper nacelle where each of the propulsion motors is sized to deliversufficient power for HOGE. An extra propulsion motor 216C is alsoincluded, possibly disposed between the nacelles in a wing or fuselageof the aircraft. Motor 216C also electrically couples to electricalenergy source 220 via an electrical cable 225. Motor 216C can alsomechanically couple to rotors 205 via drive cross shafts 218C. Extrapropulsion motor 216C preferably has at least equal power to that ofmotors 214C to ensure that HOGE can be achieved in OPMI conditions evenwhen one of motors 214C are inoperative.

FIG. 2D illustrates driveline 200D, which is considered to have aminimalist safety approach. While motors 214D can provide HOGE underdesirable conditions, OPMI is expected to be achieved with autorotation.As illustrated, only one of motor 214D is housed within nacelles 240,where motors 214D drive rotors 205 via reduction gearboxes 212D.

The above four driveline options are presented to illustrate variousdesign possibilities afforded by an E-VTOL aircraft. One shouldappreciate that many other configurations for a driveline are possible,all of which are contemplated. Furthermore, one should note that thedrivelines can lack cross shafts coupling the motors to the rotor, orlack a shifting gearbox as is typical in traditional combustion-baseddesigns of efficient tilt rotors as opposed to inefficient tilt rotoraircraft (e.g., the V-22).

Combining the approaches outlined above for propulsion systems anddrivelines confers many abilities or capabilities to an E-VTOL aircraft.By providing the ability to safely achieve HOGE while under electricalpower, contemplated E-VTOL aircraft can be used or otherwise operate inbuilt-up or populated arenas. The aircraft have low levels of noise andlow level emissions. An all electric, quiet vertical propulsion systemsimply produces no unacceptable location emissions during verticalflight regime or initial climb.

E-VTOL aircraft based on the disclosed systems can provide for amarket-viable purebred all-battery configuration, where the aircraft canhave a range in excess of 200 nm with a vertical ascent within threeminutes. Such an aircraft can also have descent and powered verticallanding reserves of at least one minute.

A heavy hybrid having a battery-only range in excess of 50 nm couldoperate locally to and from a logistically unsupported base. These basesare expected to provide electrical recharge energy to recharge the heavyhybrid's batteries.

Contemplated configurations also lack a requirement for a 2-speedgearbox normally required to efficiently match the large variation inrequired rotor RPM between hover and cruise operation modes due to poorturn-down fuel consumption of typical turbine-powered rotor withmechanical drive trains using fixed ratio gearboxes. Rather, thecontemplated designs exploit the large turndown required in rotor RPMfor cruise efficiency without a multi-speed gearbox.

The contemplated designs have safety exceeding that of conventionalmechanical driveline rotary-wing aircraft. For example, the contemplateddesigns not only have a normal innate ability to provide safeauto-rotation upon loss of all drive power, the electrically propelledrotorcraft hybrids can descend for controlled battery-powered hover orvertical landing after loss of a sustainer energy/power source (e.g.,larger batteries, fuel-cells, semi-cells, engine/generator, etc.). In asimilar vein, hybrids can hover or land vertically using the sustainerenergy/power source should the batteries become debilitated. Theelectrically propelled purebred battery-powered tilt-rotor or hybridrotorcraft in battery mode can perform powered hover or vertical landingafter partial battery debilitation because the batteries can be splitinto sections for electrical isolation of a failed battery section. Thesame reasoning applies to elimination of the dead man's zone duringtakeoff or landing, particularly in built-up areas.

Light propulsion motor weight (e.g., less than 0.35 lbs/shp 4-minuteoutput) allows for installation of at least two full-lift powerpropulsion motors per nacelle. In some embodiments, a nacelle couldhouse at least three half-lift power propulsion motors in each rotornacelle without requiring mechanical cross-shafting to share load whileunder OPMI during terminal operations. Such an approach is consideredadvantageous in conditions where the dead man's curve or auto-rotationcreates unacceptable risk in built-up areas. See FIGS. 2A through 2D forexample motor-nacelle configurations.

Contemplated E-VTOL aircraft have altitude-independent maximumcontinuous power from electric propulsion limited by continuous poweravailable from the batteries or from sustainer energy/power sources.E-VTOL aircraft lack a requirement for coupling rotor/propulsion motorRPM from a sustainer RPM if such a sustainer relies on rotatinggenerators, thus simplifying design or implementation criteria.Additionally, the designs also eliminate a requirement for multiple axisthermal engine operation in hybrids, hence removing special designrestrictions for multi-axis lubrication on typical nacelle mounted tiltrotor engines.

For operations in built-up areas with civilian personnel, the electrictilt-rotor will, as with other rotary wing aircraft, keep disk loadingbelow 15 lbs/sq ft for outwash velocity reasons and rotor tip speedbelow Mach 0.7 at sea level in a standard atmosphere for acousticreasons. Such a configuration allows for achieving HOGE while generatingless than 40 dB of sound as measured by an observer on the ground 1,500feet from the aircraft.

Bases of Performance

FIG. 3 presents a table that is considered to list market-competitivecapabilities of viable E-VTOL aircraft. The inventive subject matter isthought to depend on the capabilities, which are experimentallydemonstrated or thoroughly vetted state-of-the-art configurations,structures, electric propulsions, energy converters (where applicable),and energy storage (e.g., battery charge, high-pressure gaseous fuel, orsolid or liquid fuel) or autonomous flight control/management.

Feasibility

In order to illustrate that the vehicle assemblage can be fabricated byone practiced in the art, Sierra Marine™, Inc., was contracted toconfigure an airframe which would accommodate the light hybrid energysource. The same airframe could also accommodate a heavy hybrid or anall-battery purebred.

FIG. 4 shows the layout of a six-place, cabin class, 7,300 lb grossweight tilt-rotor. FIGS. 5, 6, 7, and 8 add detail to assure dimensionalpracticality. FIGS. 9A and 9B provide a table having a weight breakdownemploying the electrical power and drive system, including electricpropulsion, motors, cabling, and turbine/generator, designed undercontract by a major aerospace supplier. Empty weight fraction excludingenergy power pack is 48%. Battery pack is assumed to provide at least133 W-hr/kg usable energy density for 4 minutes of hover/climb/landingpower. FIG. 10 estimates hover performance, out of ground effect. FIGS.11A, 11B, and 12 provide an estimated check on lift-to-drag ratio toassure that 15:1 is easily achieved.

Based on the above parameters and with the weight breakdown from thetable of FIGS. 9A and 9B, an embodiment having the illustrative 7,300lb, 6-place, light hybrid would cruise at 18 kft and 210 kts with arange of over 1200 nm with one minute controlled vertical electricreserve for landing. Alternatively, holding the electrical propulsionaspects and gross weight of the airframe the same, but quadrupling sealevel turbine size/power and nudging up generator size to 460 kWcontinuous output from the previous continuous 400 kW, enablesover-the-weather cruise at 37,000 ft altitude and 300 kts with a 25%sacrifice in range to nearly 900 nm.

An all-battery embodiment of a purebred variant would require at leastabout 319 kW output from the batteries for 210 kts at 18 kft altitude.Allowing for 4 minutes of takeoff, initial climb to 4,500 ft, andreserve for landing at 600 kW of draw power for 540 shaft kWs ofmulti-motor output, the purebred could achieve nearly 250 nm of rangewith 1 minute powered vertical reserve using 400 W-hrs/kg (usable)batteries.

The same airframe configured as a heavy hybrid with 50 nm, 6,000 ftaltitude, 165 kt, battery-only range using 200 W-hr/kg (usable)batteries could achieve a total range of 720 nm by climbing to 18 kftaltitude and cruising at 210 kts on its sustainer energy/power source.Such an embodiment could employ the same turbine and generator asutilized in the 18 kft, 210 kt light hybrid above.

One should note that performance varies widely among the three exemplaryaircraft, depending on sustainer energy/power source, making the twohybrids more appropriate for the higher performance demands oflight-business up through cargo and charter applications. The purebredbattery electric version could be limited to personal aircraftapplications until battery technologies develop further.

The airframe weights and Optimum Speed Tilt Rotor (OSTR) performancesare based on and adapted from the demonstrated performance of DARPA'sall-carbon A160 Hummingbird of the same approximate 6,000 lb grossweight and 6 lb/sq ft disk loading. The ultra high performance electricmotors, controller/inverter, and generators/rechargers, cabling,switching, etc. are based on demonstrated proprietary aerospace industrydesigns under contract to the assignee of this application. A small (950shp) gas turbine can be based on the Army's (AATD) Small Heavy FuelEngine (SHFE) development program as demonstrated by Honeywell™Rechargeable battery performance is drawn from near-term developments byseveral suppliers (e.g., LG and A-123) currently maturing products underthe automotive plug-in hybrid programs scheduled for introduction by the2011 automotive model year. Higher performance battery estimates comefrom bench chemistry at various National Laboratories and the highestfrom Sion™, which projects >400 W-hrs/kg from LiS and has demonstrated350 W-hrs/kg, though with only 100 cycle life. Aerodynamics estimatesare based on the tilt-rotor vehicles in the thoroughly vetted JointHeavy Lift (JHL) design competition and the Army's baseline designdesignated High Efficiency Tilt Rotor (HETR).

Completely autonomous flight control/management of rotary-wing aircrafthas been demonstrated in the A160 Hummingbird and Northrop Grumman™ MQ-8Fire Scout unmanned military rotorcraft. Recharge of batteries duringflight for the hybrid configurations can of course be utilized, butpowered terminal operations (e.g., takeoff, climb, landing, etc.) do notrely on recharge for safe operation in the event of sustainer failure.

Additional Considerations

The disclosed inventive subject matter makes strides over known art bycombining various subsystems in manners that achieve unexpected results.Ordinarily, designers would avoid using a plurality of electric drivemotors within a VTOL aircraft due to the complexities of de-clutchingsuch motors from a combining gearbox after motor failure. However, theapplicants have appreciated that the benefits far outweigh theinefficiencies.

The inventive subject matter is considered to include at least threearchitectures of electrically driven vertical take-off and landing(VTOL) aircraft which are (1) politically compatible in safety, noise,exhaust emissions, and outwash velocity with terminal operations(powered hovering, VTOL) in densely populated built-up locales, (2)market competitive in range and speed, with existing equivalent class,fixed-wing and rotary-wing aircraft, (3) basing-independent to a degreeby reliance on electric energy recharge instead of entirely on onboardelectrical generators using logistic fuels, and which are variouslycomposed of previously demonstrated, independently vetted, technicallyequivalent, aerodynamically efficient, lightweight airframes, efficientmulti-RPM rotors, lightweight reduction gears, high power densityelectric drive motors and generators, high energy and power densitybatteries, efficient lightweight engines and fuel cells, and autonomousflight management systems.

One should appreciate that presented concepts also allow for E-VTOLaircraft having the following characteristics as discussed above:

-   -   An electric motor-driven, high aspect ratio (>12) tilt-rotor        aircraft, with glide ratio ≧14, cruise rotor propulsive        efficiency ≧0.85, empty weight fraction ≦0.50 (absent electrical        energy/power package source)    -   A plurality of electric drive motors for each rotor with each        motor of sufficient power that one propulsion motor inoperative        (OPMI) will not prevent hover-out-of-ground-effect (HOGE) and        will allow continued HOGE without the requirement for propulsion        cross-shafting,    -   For light-hybrid electric power train architecture, sufficient        rechargeable electric energy storage (e.g., battery) at ≧100        W-hrs/kg (usable) to enable 3 minutes of take-off and climb and        1 minute of landing, all at HOGE power draw, and power capacity        to execute 30 second vertical landing with half electrical        energy storage inoperative, all without recourse to non-stored        electrical sustainer energy/power    -   For heavy-hybrid electric power train architecture, sufficient        rechargeable stored electric energy (e.g., battery) at ≧200        W-hrs/kg (usable) to enable ≧50 nm range without recourse to        non-stored electrical sustainer energy/power    -   For purebred electric power train architecture, sufficient        rechargeable stored electric energy (e.g., battery) at ≧400        W-hrs/kg (usable) to enable, ≧200 nm range with no non-stored        electrical sustainer energy incorporated in the power        architecture    -   Rotor tip velocity ≦0.7M, and    -   Disk loading ≦15 lbs/sq ft.

Due to the fertile inventive ground surrounding the presented concepts,the inventive subject matter is considered to include additionalconcepts or variations on the presented concepts.

Table 3 includes a possible set of claims directed to a VTOL aircrafthaving a plurality of motors coupled to a rotor. Should one of themotors fail, one or more of the remaining operative motors can beconfigured to drive the rotor.

TABLE 3 Claim Set A 1 A vertical takeoff and landing (VTOL) heavier thanair aircraft, comprising: at least a plurality of electric motorscoupled to a first rotor of the aircraft where the remaining operativemotors are capable of driving the first rotor upon failure of one motor;an electrical energy store coupled to the motors; and wherein theaircraft is capable achieving hover-out-of-ground-effect (HOGE) withinat least four minutes with one propulsion motor inoperative (OPMI) usingthe electrical motor(s) while carrying a payload of at least 50 pounds.2 The aircraft of claim 1, wherein the plurality of motors couple to asecond rotor of the aircraft where the remaining operative motors arecapable of driving the second rotor upon failure of one motor. 3 Theaircraft of claim 2, wherein the aircraft lacks a cross shaft couplingthe motors to the separate rotors. 4 The aircraft of claim 2, whereinthe aircraft lacks a multi-speed gearbox. 5 The aircraft of claim 2,wherein the first and the second rotors correspond to a first and asecond nacelle, respectively; the first and second nacelles housing aplurality of motors, separately or in combination, each nacelle capableof four minutes of HOGE power after OPMI. 6 The aircraft of claim 2,wherein the rotors are tiltable 7 The aircraft of claim 1, wherein theaircraft is capable of achieving HOGE while generating less than 120 dBof sound. 8 The aircraft of claim 1, wherein the rotor is tiltable.

Table 4 provides a possible claim set describing a method of providing aVTOL aircraft having a reduced “dead man's zone”. The VTOL aircraft isconfigured to comply with one or more safety metrics that would beconsidered improvements over existing aircraft designs, including fixedwing aircraft. An individual, possibly a buyer of an aircraft, can bepresented a comparison of the VTOL aircraft with that of other aircraftto allow the individual to make informed decisions.

TABLE 4 Claim Set B 1 A method of providing a vertical takeoff andlanding (VTOL) heavier than air aircraft having a reduced “dead man'szone”, comprising: providing a design for a VTOL aircraft comprising atleast one rotor; coupling a plurality of redundant electrical motors tothe at least one rotor; coupling an electrical energy store to theplurality of electrical motors in a manner sufficient for the aircraftto hover out of ground effect for at least four minutes with OPMI;configuring the VTOL aircraft to comply with a plurality of safetymetric, including a dead man's zone; and presenting an individual with acomparison of at least one safety metric, including the dead man's zone,of the VTOL aircraft to a second safety metric of a second, differentaircraft having a design that is different from the VTOL aircraft. 2 Themethod of claim 2, the method of claim 1 wherein the at least one safetymetric comprises an estimated metric. 3 The method of claim 2, whereinthe at least one safety metric comprises accidents per flight-hour. 4The method of claim 2, wherein the at least one safety metric comprisesfatalities per flight-hour. 5 The method of claim 2, wherein the secondaircraft comprises a fixed-wing aircraft. 6 The method of claim 1,further comprising coupling the plurality of electric motors to at leasttwo rotors and to the electrical energy store. 7 The method of claim 1,further comprising adapting the aircraft to recharge the electricalenergy store while in flight under power of a fuel driven engine.

Table 5 provides another possible claim set where an electricallypowered VTOL aircraft has various possible ranges and cruising speeds.

TABLE 5 Claim Set C 1 A vertical takeoff and landing (VTOL) heavier thanair aircraft, comprising: a plurality of electric motors, each coupledto a plurality of rotors; an electrical energy store coupled to each ofthe motors; and wherein the aircraft can carry a payload of at least 200pounds for a range of at least about X nautical miles (nm) at a cruisingspeed of up to about Y knots, where X is 200 and Y is 165 knots. 2 Theaircraft of claim 1, wherein X is 800 nm and Y is 340 knots. 3 Theaircraft of claim 1, wherein X is 800 nm and Y is 300 knots. 4 Theaircraft of claim 1, wherein X is 800 nm and Y is 210 knots.

Table 6 provides an additional claim set where a contemplated VTOLaircraft comprises a sustainer energy source capable of driving anelectric motor of a rotor.

TABLE 6 Claim Set D 1 A vertical takeoff and landing (VTOL) heavier thanair aircraft, comprising: an electric motor coupled to a rotor; anelectrical energy store coupled to the motor; a sustainer energy sourcecomprising at least one of a rotating generator, electric fuel cell, orelectric semi-cell, and that is electrically coupled to the electricmotor; and wherein the electric motor is mechanically decoupled from thesustainer power supply. 2 The aircraft of claim 1, wherein the sustainerenergy source is fuel driven. 3 The aircraft of claim 1, wherein theelectric motor is within a nacelle of the rotor, and wherein thesustainer energy source is external to the nacelle. 4 The aircraft ofclaim 1, wherein the rotor is tiltable.

Table 7 presents a possible claim set relating to a VTOL aircraft wherea sustainer energy source retains a preferred orientation relative to afuselage of the aircraft as the rotors of the aircraft tilt.

TABLE 7 Claim Set E 1 A vertical takeoff and landing (VTOL) heavier thanair aircraft, comprising: an electric motor coupled to a tiltable rotor;an electrical energy store coupled to the motor; and a sustainer powersupply providing electrical power to the electric motor where thesustainer power supply retains a preferred orientation relative to afuselage of the aircraft as the rotor tilts. 2 The aircraft of claim 1,wherein the rotor is engaged with a tiltable nacelle. 3 The aircraft ofclaim 2, wherein the electric motor is housed within the nacelle. 4 Theaircraft of claim 2, wherein the sustainer power supply is external tothe nacelle. 5 The aircraft of claim 1, wherein the sustainer powersupply is configured to retain the preferred orientation relative to thefuselage of the aircraft during flight.

Thus, specific compositions and methods of the inventive subject matterhave been disclosed. It should be apparent, however, to those skilled inthe art that many more modifications besides those already described arepossible without departing from the inventive concepts herein. Theinventive subject matter, therefore, is not to be restricted except inthe spirit of the disclosure. Moreover, in interpreting the disclosureall terms should be interpreted in the broadest possible mannerconsistent with the context. In particular the terms “comprises” and“comprising” should be interpreted as referring to the elements,components, or steps in a non-exclusive manner, indicating that thereferenced elements, components, or steps can be present, or utilized,or combined with other elements, components, or steps that are notexpressly referenced.

What is claimed is:
 1. A vertical takeoff and landing (VTOL) heavierthan air aircraft, comprising: at least a first electric motor coupledto a first rotor configured to produce a thrust force counter to aweight of the aircraft; at least one electrical energy store coupled toat least the first electric motor; and wherein the aircraft is capableachieving hover-out-of-ground-effect (HOGE) for a period of at leastfour minutes while the first electric motor drives the first rotor toproduce the thrust, and while the aircraft carries a payload of at least50 pounds.
 2. The aircraft of claim 1, wherein the electrical energystore comprises a rechargeable battery.
 3. The aircraft of claim 2,wherein the rechargeable battery is repositionable within the aircraftfor center of gravity adjustment.
 4. The aircraft of claim 1, furthercomprising at least one sustainer energy source configured to generateelectricity to power the first electric motor to drive the rotor.
 5. Theaircraft of claim 4, wherein the sustainer energy/power source comprisesat least one of the following: a fuel driven engine with a generator, afuel cell, and a semi-cell.
 6. The aircraft of claim 4, wherein the atleast one energy store is configured to be recharged from the sustainerenergy/power source.
 7. The aircraft of claim 1, wherein the at leastone electrical energy store is configured to deliver at least 100W-hrs/kg.
 8. The aircraft of claim 1, wherein the aircraft is capable offlight to a range of at least 200 nautical miles without requiringnon-stored electrical sustainer power.
 9. The aircraft of claim 1,wherein the payload is at least 3,500 pounds.
 10. The aircraft of claim1, wherein the first rotor has a maximum tip speed of less than Mach 0.7M at sea level in a standard atmosphere.
 11. The aircraft of claim 1,wherein aircraft has a maximum disk loading of less than about 15 lbs/sqft.
 12. The aircraft of claim 1, wherein the aircraft is unmanned. 13.The aircraft of claim 1, wherein the first rotor is tiltable.
 14. Theaircraft of claim 13, further comprising a sustainer energy/power sourceconfigured to retain a preferred orientation relative to a main body ofthe aircraft as the rotor tilts.
 15. The aircraft of claim 1, furthercomprising a second electric motor coupled to the at least oneelectrical energy store, where the second electric motor is coupled to asecond rotor.
 16. The aircraft of claim 15, wherein the first electricmotor is coupled to the second rotor and is configured to drive thesecond rotor upon failure of the second electric motor.
 17. The aircraftof claim 16, wherein the aircraft is capable of achieving HOGE where oneof the first and second electric motors is inoperative.
 18. The aircraftof claim 15, wherein the first and the second electric motors are housedin respective first and second nacelles, where the first and secondnacelles each house a plurality of electric motors, and where each motorof the nacelle is sized and configured to allow the aircraft to sustainHOGE after failure of the first or the second electric motors.
 19. Theaircraft of claim 15, wherein the aircraft lacks a cross shaft couplingthe motors to the rotors.
 20. The aircraft of claim 15, wherein theaircraft lacks a shifting gearbox.
 21. The aircraft of claim 1, whereinthe aircraft is capable of achieving HOGE while generating less than 40dB of sound as measure by an observer on the ground 1,500 feet away fromthe aircraft.
 22. The aircraft of claim 1, wherein the at least oneelectrical energy store is field replaceable.